Tidal Power Technology

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Dam of the tidal power plant on the estuary of the Rance River, Bretagne, France. Dani 7C3/WIKIMEDIA COMMONS (cropped and used under CC BY-SA 3.0)

When thinking of renewable energy sources, people generally think of solar, wind and water. But, there's a new energy source that is emerging on the market: the moon.

As you probably know, the Earth's tides are generated by the gravitational pull of the moon. The idea of using this natural occurrence as a source of energy is not new. In fact, farmers used water mills powered by tides as early as the Middle Ages. Now, as the demand for clean sources of energy increases and technology continues to develop, researchers are looking to tidal barrages and turbines to help supplement energy to the grid.

A tidal barrage is similar in structure to a typical dam, except water can flow through it in both directions. The barrages are outfitted with turbines, and as the ocean transitions from low tide to high tide, water flows through the turbines causing them to rotate. This rotational motion in turn powers a motor which produces electricity. Once the water level is at high tide, the openings can either be closed or left open. If they are closed, then they are not reopened until the water on the other side drops to a lower level. At this time, the gates are opened and energy is produced at a controlled rate as water passes back through the barrage turbines. If the gates are not closed, then energy will be produced at the end of the high-tide period as water naturally recedes slowly to a normal level. This reversible aspect of tidal barrages sets them apart from wind turbines, which can only operate in one direction.

tidal power barrage

There are some drawbacks to this form of tidal power. A possible environmental concern is that construction of barrages might detrimentally impact coastal habitats for ocean organisms. A second type of tidal power addresses this problem by using tidal currents instead of the energy generated by the change in water level. Tidal turbines function in the same way as they do in a barrage, except their rotation is slower and caused by the currents created during the changing tides. Because there is no barrage, ocean organisms can move freely between them.

The biggest benefit of using tidal power is that, unlike wind or solar sources, it is extremely predictable. By knowing the location of the moon and the sun, we also know the motions of the tides. Therefore, with tidal power technology we could determine not only when peak energy production would occur, but how much energy we could expect to produce. Electric utilities could then decrease their outputs during these times accordingly and instead supplement the grid with energy from tidal sources. Although currently just a nascent technology, we can expect to see a lot more tidal power sources in upcoming years.

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